The present invention relates to an optical encoder used for measuring a displacement of a movable member, such as an optical shaft angle encoder or a position sensor.
Various types of optical encoders that are used to resolve the position and the movement of an object are known. FIG. 1 illustrates an example of an optical encoder disclosed in a German Laid-Open Patent Application (DE A1) No.2,316,248. The optical encoder comprises a light source 200, a lens 202 which collimates a light beam from the light source 200, a first fixed diffraction grating 204 and a second movable diffraction grating 206, a condenser lens 208 and light receiving elements 210, 212 and 214. The collimated light source 200 is incident on the first fixed diffraction grating 204 and then to a second movable diffraction grating 206. As the movable diffraction grating 206 is displaced in the direction indicated by an arrow R, the interference fringes are moved on the light receiving elements 210, 212, 214 via the condenser lens 208, resulting in a sinusoidal change in the amount of light received by the light receiving element 210, 212 and 214. Thus, if the movable diffraction grating 206 moves a single pitch of the grating, the level of output from the light receiving elements 210, 212, 214 varies like a single period of sine wave. By sensing this change, the amount of displacement of the movable diffraction grating 206 can be determined.
Another typical optical encoder which is illustrated in FIG. 2 uses a shaft encoder 300 which includes an encoding wheel 302 having plurality of slits 304 therein. A light source 306 is positioned on one side of the encoding wheel 302, while a photosensor 308, such as a phototransistor, is positioned on the other side of the encoding wheel 302 opposite to the light source 306. The rotation of the encoding wheel 302 therebetween generate a series of light pulses to be received by the photosensor 308, by which the displacement of the encoding shaft 300 can be measured.
Although such a prior art approach has worked well depending on the measuring apparatus and the precision required, the optical encoder which use diffraction gratings offers high resolution, but also expensive to manufacture and relatively complex in their design compare to the encoder wheel. However, the low cost and simplicity the encoding wheel does not generate a very high resolution that is required by some devices, there is an upper limit on the number of slits that can be incorporated in an encoding wheel.
Thus, it is desirable to provide an optical encoder apparatus that produces high resolution, low cost of manufacturing and simple in design.
It is a primary objective of this invention to provide an optical encoder in which the aforementioned disadvantages are eliminated.
Another object of the present invention is to provide a simple optical encoder without using a collimating lens.
Yet another object is to provide an optical encoder having components which can be easily manufacture.
Yet another object is to provide an optical encoder in which a light source having a wide light-emitting surface can be use.
Yet another object of the present invention is to provide a two dimensional optical encoder.
Yet another object is to provide an optical encoder that applies over a large surface area.
According to one aspect of the present invention, an optical encoder comprising:
a light source emitting a light beam;
a first array of lenslets to which the light beams is directed;
a second array of lenslets or lens to which the light beams exiting from the first array of lenslets are directed; and
a means for obtaining the displacement information of one of the first or second array of lenslets is being displaced. The displacement information is obtained by the changing position of the dark and bright patterns generated by the individual lenslets, which define the light beam into fine beams of periodic pattern or dark and bright fringes as the light beam pass through the first and second array of lenslets.
Additionally, applying the same principle can create a two-dimensional optical encoder. The method is to superpose two array of lenslets, the arrays of lenslets are arranged in such a manner that the longitudinal axis of the lenslets are perpendicular to each other. Thus, the light beam that is being defined by the first layer composes of arrays of lenslets superpose perpendicularly and the exiting beam is then directed to a second similar layer which defines the light beam into two sets of dark and bright fringes. Thus generating a two dimensional optical encoder.
Another feature of the present invention is that array of lenslets can be manufactured quite economically in a large array size. Thus, the present invention is ideal for applications that require an optical encoder that covers a large surface area. An example of such application is an optical pen or mouse.
According to another aspect of the present invention, an optical encoder comprising:
a light source emitting a light beam;
a movable lenticular array to which the light beams is directed. The light beam passes through each individual lenslets which defines the light beam into a fine beam of periodic pattern;
a means for detecting the light pattern and measuring the output signal as the lenticular array is being displaced.
Similarly, a two-dimensional optical encoder can be obtained by superposing two lenticular arrays having the longitudinal axis of the lenslets arrange perpendicularly to each other.